The present disclosure relates to a liquid crystal display device. Liquid crystal display devices are used in various fields for being thin and light-weighted. In particular, the number of liquid crystal display devices installed in a vehicle is increasing as automobiles are equipped with more electronics. In many cases, if the display device needs to have a wide viewing angle, a lateral electric field liquid crystal display device is used.
Because automobiles are used in a very wide range of temperature, the required operation temperature range for a liquid crystal display device is −30 degrees C. to 80 degrees C., which is very wide. Recently, some vehicles have started to use liquid crystal display devices for side mirrors, a rear-view mirror, and the like. Because the liquid crystal display device needs to smoothly display an image from a camera installed outside the vehicle, a sufficient level of response speed is required in the overall temperature range.
The response speed of the liquid crystal display device slows down as the temperature goes down, but the liquid crystal display device is required to have a response speed necessary to display a video even in a low temperature range. The response speed is generally represented by the sum (τon+τoff) of the leading time (τon) and the trailing time (τoff). Thus, it is necessary to reduce both the leading time and trailing time.
The response speed is improved by reducing the viscosity of the liquid crystal material or reducing the gap in the liquid crystal layer. However, those methods are not enough to achieve a sufficient response speed. When a pixel voltage is applied (ON period), the response speed of the liquid crystal is determined by the relationship between the elastic energy of the liquid crystal and the resistant voltage. When no voltage is applied (OFF period), the response speed of the liquid crystal is the recovery speed of the liquid crystal by the elastic energy. The leading time can be reduced with the overdrive. On the other hand, the trailing speed is determined by the natural recovery force of the elasticity, and with a normal cell structure, it is not easy to reduce the recovery speed.
The starting point of the recovery of the liquid crystal from the OFF state is the liquid crystal molecules having a fixed orientation by alignment films each disposed above and below the liquid crystal layer. Thus, by increasing the number of this starting point to help the liquid crystal molecules return to the initial state, the liquid crystal can recover from the OFF state faster, which improves the response speed. In relation to this point, U.S. Pat. No. 6,452,657 discloses a specific IPS (in-plane switching) structure, for example. In this structure, the orientation of the liquid crystal molecules in the sub-sections surrounded by the driving electrode and common electrode in each pixel differs from each other, and because the liquid crystal molecules in the borders of the sub-sections that do not rotate and remain stable function as walls, it is possible to improve the response speed.